1. Field of the Invention
The present invention relates generally to a wireless communication system, and in particular, to a transmission/reception apparatus using transmission antenna diversity to compensate for degradation due to fading.
2. Description of the Related Art
In a wireless communication system, time and frequency diversity is one effective techniques for suppressing fading. Among known techniques for antenna diversity, a space-time block code proposed by Vahid Tarokh extends transmission antenna diversity proposed by S. M. Alamouti so that two or more antennas can be used. The proposal made by Tarokh is disclosed in a paper “Space Time Block Coding From Orthogonal Design,” IEEE Trans. on Info., Theory, Vol. 45, pp. 1456-1467, July 1999, and the proposal made by Alamouti is disclosed in a paper “A Simple Transmitter Diversity Scheme For Wireless Communications,” IEEE Journal on Selected Area in Communications, Vol. 16, pp. 1451-1458, October 1998.
FIG. 1 is a block diagram illustrating a structure of a transmitter using a space-time block code according to the prior art. The transmitter is proposed by Tarokh, and as illustrated, is comprised of a serial-to-parallel (S/P) converter 110 and an encoder 120. In this structure, the transmitter uses three antennas 130, 132 and 134.
Referring to FIG. 1, the S/P converter 110 groups 4 input symbols into one block, and provides the block to the encoder 120. The encoder 120 makes 8 combinations with the 4 symbols, and delivers the 8 combinations to the 3 transmission antennas 130, 132 and 134 for 8 time intervals. The 8 combinations can be expressed in an 8×3 encoding matrix which is defined as
                              g          3                =                  [                                                                      s                  1                                                                              s                  2                                                                              s                  3                                                                                                      -                                      s                    4                                                                                                s                  1                                                                              -                                      s                    4                                                                                                                        -                                      s                    3                                                                                                s                  4                                                                              s                  1                                                                                                      -                                      s                    4                                                                                                -                                      s                    3                                                                                                s                  2                                                                                                      s                  1                  *                                                                              s                  2                  *                                                                              s                  3                  *                                                                                                      -                                      s                    2                    *                                                                                                s                  1                  *                                                                              -                                      s                    4                    *                                                                                                                        -                                      s                    3                    *                                                                                                s                  4                  *                                                                              s                  1                  *                                                                                                      s                  4                  *                                                                              s                  3                  *                                                                              s                  2                  *                                                              ]                                    (        1        )            where g3 represents an encoding matrix of symbols transmitted via 3 transmission antennas, and s1, s2, s3 and s4 represent 4 input symbols to be transmitted.
The encoder 120 applies negative and conjugate to 4 input symbols, and outputs the result values to the 3 antennas 130, 132 and 134 for 8 time intervals. In this case, symbol sequences output to the antennas, i.e., rows, are orthogonal with one another.
More specifically, in a first time interval, 3 symbols s1, s2, and s3 in a first row are delivered to the 3 antennas 130, 132 and 134, respectively. Likewise, in the last time interval, 3 symbols s4*, s3* and s2* in the last row are delivered to the 3 antennas 130, 132 and 134, respectively. That is, the encoder 120 sequentially delivers symbols in an Mth row of the encoding matrix to an Mth antenna.
FIG. 2 is a block diagram illustrating a structure of a receiver for receiving a signal transmitted from the transmitter of FIG. 1. As illustrated, the receiver is comprised of a plurality of reception antennas 140 and 142, a channel estimator 150, a multi-channel symbol arranger 160, and a detector 170.
Referring to FIG. 2, the channel estimator 150 estimates channel coefficients representing a channel gain from transmission antennas to reception antennas, and the multi-channel symbol arranger 160 collects reception symbols from the reception antennas 140 and 142, and provides the collected reception symbols to the detector 170. The detector 170 then calculates a decision statistic for all possible symbols with hypotheses symbols determined by multiplying the reception symbols by the channel coefficients, and detects transmission symbols by threshold detection.
The space-time block coding technique proposed by Alamouti, though complex symbols are transmitted through 2 transmission antennas, obtains a diversity order equivalent to the number of transmission antennas, i.e., the maximum diversity order, without inflicting a loss on a rate. The devices of FIGS. 1 and 2 proposed by Tarokh by extending this technique obtain a maximum diversity order using a space-time block code in the form of a matrix having orthogonal rows. However, since the devices transmit 4 complex symbols for 8 time intervals, they suffer a loss of the rate by ½. In addition, since 8 time intervals are required in completely transmitting one block (having 4 symbols), reception performance become poor due to a variation in a channel environment within a block in the case of fast fading.
When complex symbols are transmitted using 3 or more antennas as mentioned above, 2N time intervals are required in order to transmit N symbols, resulting in a loss of a rate. The loss of a rate also causes an increase in latency.